Cathartics (Gr. from to cleanse), medicines used to promote evacuation of the intestines. Their number is very large, and they may be divided into several classes, such as mechanical, including unbolted meal of various kinds, fruits, and mustard seed; oily, as croton and castor oil; saline, as magnesia and its carbonate, sulphate, and citrate, sulphate and phosphate of soda, bitrate of po-tassa, etc.; acid or bitter, as rhubarb, senna, colocynth, and aloes; resinous, as jalap, scam-mony; gamboge, and podophylline; and mercurial, calomel and blue pill. Their action varies, partly with the dose, from the mild and almost natural effect of magnesia and aloes, to the violent purging of jalap, gamboge, or elate-rium. For a more detailed statement of individual peculiarities, see the several titles. - The modus operandi of cathartics is chiefly in stimulating the intestines to more active contraction, and thus either hastening the discharge of the more watery contents of the upper bowels, before they have time to experience the loss of fluid which usually takes place by absorption in the large intestine, or else unloading the colon of its normal contents.
The saline cathartics are probably always absorbed to some extent, and if they fail to act upon the bowels may be eliminated in part or wholly by the urine. Some of the others, as senna and scammony, demonstrate their occasional absorption by causing purgation in infants when taken by the nurse. The coloring matter of rhubarb sometimes appears in the secretions. - Cathartics are very largely used, both singly and in the most various combinations with each other and with tonics and aromatics, from the natural salines of mineral springs to the numerous quack compounds with which the country is flooded. They are probably more abused than any other class of drugs, since a resort to them is so easy as to often lead to a neglect of highly important hygienic rules. They should never be allowed to take the place of due attention to diet, exercise, and habit. The common use of powerful cathartics at the beginning of acute diseases, to " work off a cold " for instance, is as a rule to be deprecated. Their use, however, is often necessary, not only to relieve constipation, but to withdraw water primarily from the intestinal canal, and secondarily from other parts of the body, as in dropsy,, or to control the circulation by calling a large amount of blood into the capacious veins and arteries of the abdomen.
The uterus, from its nearness to the bowel, may be injuriously affected by the action of violent purges.